Production of artificial protein threads, fibres, filaments and the like



United States Patent PRODUCTION OF ARTIFICIAL PROTEIN THREADS, FIBRES, FILAMENTS AND THE LIKE Robert L. Wormell, Coventry, England, assignor to Courtaulds Limited, London, England, a British company No Drawing. Application July 29, 1957 Serial No. 674,586

Claims priority, application Great Britain August 24, 1956 6 Claims. (Cl. 18-54) This invention relates to the production of regenerated p'ortein threads, fibres, filaments and the like, hereinafter generally referred to as threads. The invention may be applied for example to the production of threads from milk, or lactic, casein, peanut protein, 'soya bean protein or castor bean protein. 7

It is known to produce threads from proteins by extruding an alkaline solution of the protein into a coagulating bath containing an acid, usually sulphuric acid, and one or more salts having an astringent action on the freshly extruded threads, for example sodium sulphate and aluminium sulphate. The threads are then generally hardened, that is to say, rendered insoluble in water at ordinary temperatures, stretched and hardened once more as described in British patent specification No. 502,710; finally, the threads are usually subjected to an insolubilising process which renders the threads resistant to the action of boiling water or hot aqueous solutions. An example of a convenient insolubilising process is the cyanate process described and claimed in United States Patent No. 2,684,282.

Chromium salts are known to have a pronounced hardening and insolubilising action on protein threads but they have not been used very widely on a commercial scale; before the chrome treatment can be carried out, the other salts used in coagulating and/ or hardening must first be washed out of the thread.

The object of this invention is an economic process for chrome-treating protein fibres.

According to the present invention, a process for the production of regenerated protein threads comprises extruding an aqueous alkaline solution of a protein through a jet into an acid coagulating bath in which is dissolved a trivalent chromium salt so that the bath contains the equivalent of at least grams per litre of Cr O stretching the resultant thread at least 100 percent in a salt bath at a temperature of at least 50 C. containing a trivalent chromium salt and hardening the stretched thread in a salt bath also containing a trivalent chromium salt.

The coagulating bath used contains an acid which will in general be sulphuric acid. It also contains one or more salts such as sodium sulphate and/ or aluminium sulphate which have an astringent action on the thread and so prevent it swelling and possibly disintegrating when in contact with aqueous baths. The bath should contain at least 10 grams per litre of Cr O present as a trivalent chromium salt but it is preferred to use higher concentrations of for example 25 to 50 grams/litre. The coagulating bath may be at any temperature from ordinary temperature to about 50 C.; the preferred temperature range is 38 to 43 C. Temperatures much higher than 50 C. are preferably avoided as they tend to lead to blebbing at the jet and stuck filaments. A convenient coagulating bath is one of specific gravity 1.237 at 40 C. containing 200 grams/litre of Na SQ; (i.e. anhydrous), 40 grams/litre of Cr O added in the form of Cr O(SQ and 40 grams/litre of sulphuric acid.

2,897,044 lc Patented July 28, 1959 'The stretching bath preferably has the same composition as the coagulating bath with the exception that the acid content is reduced; about 10 grams/ litre of sulphuric acid is preferred. The temperature of the bath must be at least 50 C. and temperatures of 60 to 65 C. are preferred. A suitable stretching bath has the composition 200 grams/litre of Na SO 40 grams/litre of Cr O and 10 grams/litre of sulphuric acid, this bath being used at 65 C. In a continuous run, care must be taken to adjust the composition of the bath as a result of carry-over of acid by the thread from the coagulating bath. Stretching may be effected by any known means such as by rollers of progressively increasing speeds.

The hardening bath may have the same composition as that of the stretching bath but this is not-essential. For example the chromium content may; be increased and the content of the Na SO may begg reduced; The bath may be at any temperature but raised temperatures are preferred so as to accelerate the hardening reaction. The bath may also contain other hardening agents such as formaldehyde but this is not essential.

As is customary in the production of protein threads the stretching and hardening baths contain one or more salts such as sodium sulphate and/ or aluminum sulphate which have an astringent action on the thread. The

. chromium content of the three baths used for coagulating,

stretching and hardening is preferably the same, thereby simplifying making up of the solutions and also facilitating recovery.

In a preferred folm of the invention, a heat-stabilising step is introduced between the stretching and hardening stages. The heat stabilising process consists in holding the threads under tension, but without stretching, for up to one minute in one or more salt baths containing a trivalent chromium salt at a temperature of at least 60 C. The heat stabilising bath may conveniently be the same as that used in the stretching stage. Such a heat stabilising step serves to allow the fibres to absorb chromium and become cross-linked and hence more stable. A suitable stabilising treatment may be fore 9 seconds at C. followed by 9.5 seconds at C., the thread during the treatment being held under tension, but without stretching, between rollers rotating at equal speeds.

Any of the water-soluble trivalent chromium salts may be used, for example chromium sulphate, chrome alum or basic chromium sulphate. When basic chromium sulphate is used, allowance must be made in making up the baths for the sodium sulphate which it contains.

Treatment of long lengths'of continuous threads may conveniently be effected using the plaiting method de-' scribed in United States Patent No. 2,3 83,358.

The threads obtained by the present invention contain chemically combined chromium and have a marked resistance to hot liquids but, if desired, the threads may be subjected to a further hardening treatment with or without a chromium salt, or a known insolubilising process such as a cyanate treatment as described in United States Patent No. 2,684,282. The combined chromium improves the fire resistance of the threads.

The invention is illustrated by the following examples in which percentages are by weight.

In certain of the examples the water imbibition of threads made in accordance with the invention is given. Water imbibition is a measure of the degree to which water is taken up by the threads. The term is well known in the art and is defined, for example, in my prior Patent 2,691,568, granted October 10, 1954, as the percentage by weight of water retained on the oven-dried fiber after centrifuging a 0.5 g. sample for 5 minutes at 1000 g.

Example 1 A dispersion of 18 percent of lactic casein in 1 percent aqueous caustic soda solution was extruded into a coagulating bath at 40 C. containing, in each litre, 150 grams of sodium sulphate, 40 grams of sulphuric acid,

and basic chromium sulphate (Cr O(SO equivalent 7 per litre of formaldehyde added.- The threads were then washed and dried.

The threads obtained were pale blue in colour and showed a good resistance to boiling dilute acid and mild alkaline solutions.

Examples 2 to A dispersion of 18 percent of lactic casein in 1 percent aqueous caustic soda was extruded into a coagulating bath at 43 C. containing in each litre 200 grams/litre of Na SO (including 25 grams from the commercial chromium sulphate, green liquor), 40 grams/litre of Cr O as basic chromium sulphate and 40 grams/litre of sulphuric acid. The threads so produced were then stretched 800 percent in a bath at 65 C. containing 200 grams/litre of Na SO 40 grams/ litre of Cr O and grams/litre of sulphuric acid. The threads were then heat-stabilised on two pairs of even-speed rollers for 9 seconds and 9.5 seconds respectively, the first pair of rollers rotating in the stretch bath liquor at 80 C. and the second pair in the same liquor at 90 C.

The heat-stabilised threads were then subjected to hardening treatments as follows:

Example 2 The threads were hardened by immersion for 1 /2 hours in a bath at 65 C. having the same composition as the stretch bath liquor but with the addition of 20 grams/ litre of formaldehyde. The threads were then washed and dried. The Water imbibition of the product was 5 8.

Example 3 The threads were hardened by immersion for 1 /2 hours in a bath at 65 C. having the same composition as the stretch bath liquor but with the concentration of the Na SO raised to 300 grams/ litre. The threads were then washed and dried. The water imbibition of the product was 71.

Example 4 The threads were hardened by immersion for 30 minutes in a bath at 70 C. containing, per litre, 300 grams of Na SO 10 grams of sulphuric acid, 60 grams of crystalline aluminum sulphate, Al (SO l8H O, 40 grams of Cr O and 20 grams of formaldehyde. The threads were then washed and dried. The water imbibition of the product was 77.

Example 5 The threads were hardened by immersion for 1 hour in a bath at 65 C. having the same composition as the bath used in Example 4 except that the Na SO content was reduced to 125 grams/litre. The threads were then washed and dried. The water imbibition of the product was 68.

Examples 6 to 8 In these examples, the spinning, stretching and heatstabilising were as set out above for Examples 2 to 5.

Example 6 The threads were hardened by immersion for 4 hours Example 7 A The threads were hardened by immersion for 2 hours in a bath at 65 C. containing, in each litre, 208 grams of Na SO 68 grams of Cr O 10 grams of sulphuric acid and 20 grams of formaldehyde. The threads, after washing and drying, had an imbibition of 67 and contained 2.0 percent combined chromium.

Example 8 The threads were hardened by immersion for 1 hour in a bath at 65 (3., containing, in each litre, 223 grams of Na SO 58 grams of Cr O 10 grams of sulphuric acid and 20 grams of formaldehyde. The threads, after washing and drying, had an imbibition of 67 and contained 1.6 percent combined chromium.

Example 9 The spinning, stretching and heat-stabilising were carried out as described for Examples 2 to 5 and the heat stabilised threads were cut to staple lengths. The cut fibres were fed on to a conveyor belt and the hardening liquor described in Example 4 but at C. was continuously sprayed onto the moving fibres over a period of 20 minutes. The fibres were then washed and dried.

What I claim is:

'1; A process for the production of regenerated protein threads which comprises extruding an aqueous alkaline solution of a protein chosen from the group consisting of lactic casein, peanut protein, soya bean protein and castor bean protein through a jet into a sulphuric acid coagulating bath in which is dissolved a trivalent chromium salt, stretching the resultant thread at least percent in a stretching bath at a temperature of at least 50 C., said bath containing a trivalent chromium salt and at least one salt chosen from the group consisting of sodium sulphate and aluminium sulphate and hardening the stretched thread in a hardening bath also containing a trivalent chromium salt and at least one salt chosen from the group consisting of sodium sulphate and aluminium sulphate, the coagulating, stretching and hardening baths each containing the equivalent of at least 10 grams per liter of Cr O 2. A process as claimed in claim 1 and comprising the steps of heat-stabilising the threads, between the stretching and hardening steps, by holding them under tension but without stretching for up to one minute in at least one bath at a temperature of at least 60 C.

containing a trivalent chromium salt and at least one 'salt chosen from the group consisting of sodium sulphate and aluminium sulphate.

3. A process as claimed in claim 2 wherein the heatstabilizing bath has the same composition as the stretching bath.

4. A process as claimed in claim 1 in which the chromium content of the stretching bath and of the hardening bath is not less than that in the coagulating bath.

5. A process as claimed in claim 4 wherein the chromium content of the baths used for coagulating, stretching and hardening are the same.

6. A process as claimed in claim 1 wherein the hardening bath also contains formaldehyde.

References Cited in the file of this patent UNITED STATES PATENTS 2,297,397 Ferretti Sept. 29, 1942 2,342,994 Atwood Feb. 29, 1944 2,409,475 Cline Oct. 15, 1 946 

1. A PROCESS FOR TTHE PRODUCTION OF REGENERATED PROTEIN THREADS WHICH COMPRISES EXTRUDING AN AQUEOUS ALKALINE SOLUTION OF A PROTEIN CHOSEN FROM THE GROUP CONSISTING OF LACTIC CASEIN, PEANUT PROTEIN, SOYA BEAN PROTEIN AND CASTOR BEAN PROTEIN THROUGH A JET INTO A SULPHURIC ACID COAGULATING BATH IN WHICH IS DISSOLVED A TRIVALENT CHROMIUM SALT, STRETCHING THE RESULTANT THREAD AT LEAST 100 PERCENT IN A STRETCHING BATH AT A TEMPERATURE OF AT LEAST 50* C., SAID BATH CONTAINING A TRIVALENT CHROMIUM SALT AND AT LEAST ONE SALT CHOSEN FROM THE GROUP CONSISTING OF SODIUM SULPHATE AND ALUMINUM SULPHATE AND HARDENING THE STRETCHED THREAD IN A HARDENING BATH ALSO CONTAINING A TRIVALENT CHROMIUM SALT AND AT LEAST ONE SALT CHOSEN FROM THE GROUP CONSISTING OF SODIUM SULPHATE AND ALUMINIUM SULPHATE, THE COAGULATING, STRETCHING AND HARDENING BATHS EACH CONTAINING THE EQUIVALENT OF AT LEAST 10 GRAMS PER LITER OF CR2O3. 